Material sheets or plies may be welded together using radio frequency sealing dies or heat sealing dies. U.S. Pat. No. 8,092,631 broadly teaches using a beveled edge (e.g., chamfer) on high frequency welding dies. U.S. Publication No. 2009/0113851 teaches a seal plate with a radius on the bottom surface to create a curved profile and a chamfered edge. International Publication No. WO 2016/079702 teaches a radio frequency welding electrode with rounded sides.
Unfortunately, seal dies with chamfered edges may result in electric field concentrations at the edges of the chamfer that negatively affect seal quality. Rounded seal die profiles (e.g., with a rounded edge or radius) require a large radius to approximate linear compression between the sheets used to form a bag, which may necessitate large, heavy, expensive and less efficient RF electrode design. Additionally, rounded seal dies may reduce the amount of molten material that remains under compression beneath the rounded portion of the seal die, which may result in less cohesion between the plies of material. Further, rounded seal dies may result in a smaller bead mass, which increases the risk for stress risers due to malformed beads.
An improved die for sealing material sheets or plies is needed accordingly.